As a rotor of a motor, a rotor having a so-called Lundell structure with permanent field magnet is known. This rotor includes two rotor cores combined with each other and a field magnet arranged between the two rotor cores in an axial direction. Each of the rotor cores has a core base and a plurality of claw-shaped magnetic poles provided on an outer peripheral portion of the core base. The field magnet is magnetized in the axial direction, and the claw-shaped magnetic poles are made to function as alternately different magnetic poles. As such a rotor, a rotor provided with an auxiliary magnet illustrated in FIG. 10 of Japanese Patent Laid-Open Publication No. 2013-212036 is proposed, for example. This auxiliary magnet includes a back-surface magnet portion arranged between the claw-shaped magnetic pole and the field magnet and an inter-pole magnet portion arranged between the claw-shaped magnetic poles adjacent in the peripheral direction. The plurality of back-surface magnet portions and the plurality of inter-pole magnet portions are integrally molded so as to form an annular shape. The auxiliary magnet is magnetized so as to suppress leakage flux in a space in which the back-surface magnet portion is arranged and leakage flux in a space in which the inter-pole magnet portion is arranged.
As the auxiliary magnet (annular magnet) described above, use of a resin molding product molded by injection molding is considered. However, what kind of a resin molding product should be specifically used in order to obtain a rotor with a favorable magnetic characteristic has not been found so far.